Investment casting is widely used in the manufacture of myriad cast components including complex gas turbine engine components, such as blades and vanes made of nickel or cobalt base superalloys. In the investment casting process, a wax or other disposable pattern of the component to be cast is made typically by injecting molten wax into a pattern die cavity and solidifying the material in the die cavity. Ceramic mold material then is coated on or invested about the pattern to form a casting mold upon selective removal of the pattern by heating (melting), chemical dissolution or other conventional pattern removal technique. The ceramic investment mold typically is fired to develop mold strength, and then molten metal is cast into the mold and solidified to form the cast component, which will have the configuration of the pattern employed to make the mold.
Existing wax pattern materials normally contain a stable, solid filler material, such as for example only 4,4-isopropylidene diphenol available as Bisphenol A (BPA) or cross-linked polystyrene, which results in wax properties that limit dimensional distortion, reduce visual defects, control shrinkage, and improve dewax capabilities. Presently used filler material is a mechanically ground material that is characterized by angular surface configuration, such as an acicular particle configuration and/or fiber-like particle configuration. This filler morphology creates significant undesirable side effects which include rough and pitted casting surfaces that require extensive post-casting finishing operations and increased wax injection pressures into the pattern die cavity during pattern fabrication. Such increased wax injection pressures in the pattern die cavity can break fragile ceramic cores positioned in the die cavity and about which the wax is injected in the manufacture of wax/core pattern assemblies for use in casting hollow components, such as internally cooled turbine blades and vanes.
An object of the present invention is to provide an investment casting method conducted in a manner to improve as-cast surface of the cast component and to reduce the extent of post-casting surface finishing operations.
Another object of the present invention is to provide an improved pattern material and pattern for use in forming a refractory casting mold for use in investment casting methods.